Publication 598
taxmap/pubs/p598-010.htm#en_us_publink1000267853The unrelated business taxable income of a foreign organization exempt from tax under section 501(a) consists of the organization's:
- Unrelated business taxable income derived from sources within the United States but not effectively connected with the conduct of a trade or business within the United States,
and
- Unrelated business taxable income effectively connected with the conduct of a trade or business within the United States, whether or not this income is derived from sources within the United States.
To determine whether income realized by a foreign organization is derived from sources within the United States or is effectively connected with the conduct of a trade or business within the United States, see sections 861 through 865 and the related regulations.